The tissue-specific expression of immunoglobulin Kappa-light chain genes and heavy chain genes is associated with the enhancer sequences in these genes. Our objective is to reconstitute the tissue-specific expression of these genes extrachromosomally using a bovine papilloma virus (BPV) vector and somatic cell fusion techniques. The possibility of obtaining episomes actively expressing immunoglobulin genes should allow the study of the mechanism of tissue-specific enhancer function.